Luneberg lens with staggered waveguide feed



Oct. 1, 1968 w. J. YOUNG, JR 3,404,405

LUNEBERG LENS WITH STAGGERED WAVEGUIDE FEED Filed April 50, 1965 Fig. l

INVENTOR. WALTERJ.YOUNG,JR.

BYI

ATTORNEYS United States Patent 3,404,405 LUNEBERG LENS WITH STAGGERED WAVEGUIDE FEED Walter J. Young, Jr., Tonawanda, N.Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Apr. 30, 1965, Ser. No. 452,418 14 Claims. (Cl. 343-754) ABSTRACT OF THE DISCLOSURE An antenna array including a spherical dielectric lens and two rows of wave guides each wave guide extending from the locus of the lens focal points to a feedback wall along a respective axis passing through the center of the lens. The wave guides in one row are staggered relative to those in the other row, and each wave guide is positioned relative to the others to eliminate null points in the antenna scan wave pattern. A switch controls signal means connected to each wave guide for enabling the array to scan the wave pattern.

The present invention relates to a phased antenna array and more particularly to an antenna array using a spherical dielectric lens with a plurality of wave guides arranged around the lens wherein the arrangement of wave guides around the lens is calculated to reduce to a minimum holes in the antenna wave pattern.

In the field of antennas it has been desired to have antennas which could be scanned through an angle faster than possible by mechanical means. In order to achieve this it has been proposed to use arrays of antenna wave guides. The wave guides are switched off and on in succession causing a progression of the wavefront through the desired angle of array. In order to assist in the focus of these wave guides in a narrow beam, spherical dielectric lenses are used, either Luneberg or constant K lenses, which have the property of focusing a beam in a specified direction from a feed point either on the surface of the lens or a short distance therefrom. Among the arrangements known is that shown by Plummer, US. Patent No. 3,109,174, which shows a plurality of wave guides arranged pointing outwardly in a circle. To place a single sphere in front of each of the wave guides of an outwardly aimed circular array would involve great expense. A proposed variation would be to arrange the wave guides around a single spherical dielectric lens for a portion of the lens to provide, for example, a 30 scan angle. When this has been done it has been found that there is mutual coupling between adjacent Wave guides, causing large null points in the wave pattern, up to db or greater. The existence of these null points is a major inhibiting factor in the development of this kind of antenna array.

The general purpose of this invention is to provide an antenna array for use with a spherical dielectric lens which substantially eliminates or reduces null points in the antenna wave pattern. To attain this, the present invention contemplates a plurality of rows of wave guides positioned around a lens with each row staggered from adjacent rows by approximately one-half the angle between two adjacent wave guides. In addition each wave guide has a separate feedback wall and is adjustable longitudinally toward and away from the lens so that it may be assured that each wave guide is in phase in the scan pattern at the focal point locus of the lens.

Accordingly, it is an object of the present invention to provide an antenna array using a spherical dielectric lens with substantial elimination of null points in the wave scan pattern.

3,404,405 Patented Oct. 1, 1968 Another object of the invention is to provide an antenna array having a common phase front throughout its scan angle.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 shows a spherical dielectric lens and antenna array according to the invention.

FIG. 2 shows a section view of the wave guides taken on the line 2--2 of FIG. 1.

In FIG. 1 there is shown a spherical dielectric lens 11 attached by brackets 12 to a holder 13 which holds a plurality of wave guides 14. Each of the wave guides 14 has a signal means 15 attached and each signal means 15 is attached by a line 16 to a switch 17. The construction of wave guides 14, signal means 15, line 16, and switch means 17 is well known in the art and is not described specifically here. The purpose of switch 17 is to control the turning on and off of each of the wave guides 14 in the proper order to cause the wave pattern to rotate through the desired scan angle.

The construction of the holder 13 may be seen by reference to FIG. 2. Holder 13 comprises a top plate 21, a bottom plate 22 and two filler plates 23. In the array shown there are six wave guides 14 on the bottom row and five wave guides 14 on the top row. The five wave guides 14 on the top row are positioned in staggered formation from the ones on the bottom row exactly half way in between. As shown in FIG. 1 the front ends of each of the wave guides 14 are touching or nearly touching and each wave guide extends out longitudinally with its axis on a line with the center of sphere 11. The wave guides are clamped in the holder 13 by set screws 24 which clamp the top row of wave guides 14 onto the bottom row of wave guides 14 and then onto bottom 22. Material providing a firm non-slip surface between the bottom of wave guides 14 and the bottom plate 22 may be provided. In the example shown, the angle between the extreme left and extreme right wave guides 14 is approximately 30. Each wave guide generates a beam of approximately 5 after passage through the spherical lens. Each of the wave guides 14 may individually be positioned longitudinally with respect to the sphere to insure that its phase front is common with the phase fronts of each of the other wave guides in the array. The front end of each of the wave guides 14 is open; and the rear end of each wave guide 14 is closed, comprising the feedback wall 14a. The feed point of each wave guide is considered to be at or near its mouth, as shown in FIG. 1.

Lens 11 although shown as spherical need not be spherical where the angle of scan is very small. Other configurations of lens where desired for special purposes may be equally effective. For wide scan angles the spherical lens provides symmetrical properties for all angles of wave guide position. A Luneberg lens is a lens whose dielectric constant is not a constant throughout a sphere, but varies as a function of the radius, usually in accordance with the formula Where R is the radius of the sphere and r is the radius to any point within the sphere. With this formula, the focus of any plane wave incident on the lens is a point on its surface, and conversely, an electromagnetic signal fed to a point on the surface of the sphere will be emitted as a plane phase front from the opposite side of the sphere. Different configurations of the Luneberg lens are possible with different laws of dielectric constant varia- 3 tion to give rise to special desired properties. For example, the locus of focal points may be made to lie exterior to the physical surface in order that the wave guides may be positioned with their feed points on some surface eXterior to the sphere. Besides the Luneberg lens, another spherical lens which emits an approximately plane phase front is a spherical lens with a constant K dielectric constant which will have its focus on the surface of the sphere if the dielectric constant is approximately 3.5. If the constant is less than 3.5, the constant K spherical lens will have its locus of focal points on a sphere concentric with but exterior to the physical surface of the lens. Either the Luneberg lens or the constant K lens may be used in the array of the present invention. The constant K lens costs less to manufacture but provides very small phase aberations in the generated beam.

It will be understood that more or less than six wave guides in a row may be used. Also, more than two rows of wave guides may be used. The beam of each wave guide may be more or less than 5 depending upon the design of the particular wave guide by means Well known in the art. The beam width is defined as the angle within which the strength of the signal i within 3 db of its strength at the center of the beam.

Means other than wave guides may also be used to supply the signals to the focus of the lens. These may be any means known in the art capable of providing an electromagnetic wave feed. These may be arranged in a staggered array according to the invention to reduce mutual coupling, and may be adjusted in position to provide a common phase front.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A phased antenna array comprising:

a dielectric lens; and

a plurality of electromagnetic feeds arranged in a plurality of rows around said lens, the feeds of one row being offset with respect to the feeds of an adjacent row, each feed having a predetermined beam width, each feed being separated from each adjacent feed in the same row by said predetermined beam Width, and each feed being offset from each feed in an adjacent row by one-half of said beam width.

2. A phased antenna array as recited in claim 1 wherein said lens is a spherical dielectric lens and said feeds are located on the locus of focal points of said sphere.

3. A phased antenna array as recited in claim 2 wherein said lens has a dielectric constant varying in accordance with the formula where R is the radius of said spherical lens and r is the radius of any point inside the sphere.

4. A phased antenna array as recited in claim 2, wherein said lens has a constant dielectric constant less than 3.5.

5. A phased antenna array as recited in claim 1 Wherein said feeds are wave guides having individual feedback walls.

6. A phased antennna array as recited in claim 5 wherein said wave guides have switch means to scan said array through said rows.

7. A phased antenna array as recited in claim 6 wherein said wave guide feedback walls are longitudinally adjustable to place each wave guide feed in a common phase front during said array scan.

Cal

8. A phased antenna array as recited in claim 7 further comprising:

a bottom plate;

a bottom row of wave guides positioned on said plate;

at least one adjacent row of wave guides being positioned on top of said bottom row of wave guides, each of said wave guides being displaced laterally from the wave guides of an adjacent row by onehalf the beam width of said wave guides;

a top plate positioned above an upper row of wave guides; and

clamping means to hold said rows of wave guides between said top and bottom plates, whereby each of said wave guides is longitudinally adjustably clamped between said top and bottom plates.

9. A phased antenna array as recited in claim 8, wherein said means for clamping comprises:

a set screw in said upper plate above each wave guide in said upper row, each set screw being positioned to clamp each of said wave guides after its longitudinal adjustment.

10. A phased antenna array comprising:

a circular dielectric lens; and

a plurality of wave guides oriented in a plurality of arcuately arranged rows at the focus of said lens, each said wave guide having a predetermined beam width and being separated from adjacent wave guides in the same row by said predetermined beam width, and each said wave guide in a given row being offset from adjacent said wave guides in adjacent rows by one-half of said predetermined beam width.

11. A phased antenna array as recited in claim 10 wherein:

said wave guides each terminate in a feedback wall.

12. A phased antenna array as recited in claim 11 further comprising:

support means for adjustably supporting said wave guides in a longitudinally adjusted position for enabling said wave guides to provide a common phase front.

13. A phased antenna array as recited in claim 12 wherein said support means comprises:

a bottom plate;

a bottomrnost row of Wave guides adjustably positioned adjacent said bottom plate;

at least one other row of wave guides adjustably positioned adjacent said bottommost row of wave guides;

a top plate positioned adjacent an uppermost row of wave guides; and

adjustable clamping means connected to at least one of said plates for supporting said rows of wave guides between said top and said bottom plates whereby each of said wave guides is clamped in a longitudinally adjustable position between said top and bottom plates.

14. A phased antenna array as recited in claim 13 further comprising:

a plurality of signal means each connected to a respective said wave guide; and

switch means connected to said plurality of signal means for causing said array to scan through said rows.

References Cited UNITED STATES PATENTS 3,116,486 12/1963 Johnson et al. 343755 3,213,454 10/1965 Ringenbach 343771 3,230,536 1/1966 Cheston 343854 3,264,642 8/1966 Lamberty 343--754 3,274,601 9/1966 Blass 343-778 ELI LIEBERMAN, Primary Examiner. 

